Modeling Software Defect Introduction and Removal: COQUALMO (COnstructive QUALity MOdel)

Cost, schedule and quality are highly correlated factors in software development. They basically form three sides of the same triangle. Beyond a certain point (the “Quality is Free” point), it is difficult to increase the quality without increasing either the cost or schedule or both for the software under development. Similarly, development schedule cannot be drastically compressed without hampering the quality of the software product and/or increasing the cost of development. Watts Humphrey, at the LA SPIN meeting in December '98, highlighted that "Measuring Productivity without caring about Quality has no meaning". Software estimation models can (and should) play an important role in facilitating the balance of cost/schedule and quality. Recognizing this important association, an attempt is being made to develop a quality model extension to COCOMO II; namely COQUALMO. An initial description of this model focusing on defect introduction was provided in [Chulani97a]. The model has evolved considerably since then and is now very well defined and calibrated to Delphi-gathered expert opinion. The data collection activity is underway and the aim is to have a statistically calibrated model by the onset of the next millennium. The many benefits of cost/quality modeling include:  Resource allocation: The primary but not the only important use of software estimation is budgeting for the development life cycle.  Tradeoff and risk analysis: An important capability is to enable ‘what-if’ analyses that demonstrate the impact of various defect removal techniques and the effects of personnel, project, product and platform characteristics on software quality. A related capability is to illuminate the cost/schedule/quality trade-offs and sensitivities of software project decisions such as scoping, staffing, tools, reuse, etc.  Time to Market initiatives: An important additional capability is to provide cost/schedule/quality planning and control by providing breakdowns by component, stage and activity to facilitate the Time To Market initiatives.  Software quality improvement investment analysis: A very important capability is to estimate the costs and defect densities and assess the return on investment of quality initiatives such as use of mature tools, peer reviews and disciplines methods. This paper presents the two sub-models, i.e. the Defect Introduction and the Defect Removal sub-models, of COQUALMO. It also illustrates the integration of COQUALMO with COCOMO II to achieve the benefits outlined above.